Yahoo has filed a complaint in the San Jose courts against Facebook, saying that the social media company is infringing ten of Yahoo's patents covering areas around advertising, user actions, privacy and click fraud prevention.
The issue first came to light in February, when Yahoo told the New York Times that it was seeking a licensing deal with Facebook over "ten to twenty" of Yahoo's 1000-plus patent collection. Facebook, which is widely expected to seek an IPO in May with an estimated value of around £5bn (£3bn), said in a statement that Yahoo's actions were puzzling and disappointing, and that it would defend itself vigorously.
In 2004, Yahoo made patent claims against Google over search-related advertising, striking a deal just ahead of the Mountain View search company's own IPO.
For more on this story, see Yahoo sues Facebook over wide-ranging patents.